I gotta say your shroud looks tits. You could probably sell it once you build one that works. :) I'm gonna go take some measurements and design a shroud. I have a Koyo rad and those slim fans sitting in my room. :) Though my Koyo is the big one, which is more than 37mm IIRC.

The shroud sits on the end tank seams which are about 5/8" from the face of the rad rows, so there's a 5/8" gap from the row/surface to the shroud surface.